Stencil



Patented July 9, 1935 STENCIL Robert 0. Williams, Cleveland, Ohio, assignor of one-=third to Owen E. Williams, Baltimore, Md.,

= and one-third f ington, D. C'.

' No Drawing.

to William A. Harvey, Wash- Application September 26, 1933, Serial No; 691,097 1 1' 5 c a ms,- (01. ill-+355 This invention relates to-stencils such as are used in the reproduction of typewritten matter, Writing, drawings arid the like.

More particularly-the invention relates to a i 5 stencil sheet and the'coating for such a sheet. I

. Many of the compositions now commonly used for coating and impregnating stencil sheets are 'based onthe use of a derivative of cellulose as an essential ingredient and various objections exist to the use of this ingredient among which may be mentioned the fact that the stencil sheets to which such material is applied tend to deteriorate as they age by reason of the composition containing :the cellulose tending to harden and thereby to cause loss offiexibility and permit cracking. 1 This is. a serious objection since sheets which have :thus hardenedrcannot be properly cut, either by a typewriter or stylus, to form-the stencil. Fur :thermore, it'is frequently desirable to out such g stencils: and use them from time to time. for successive reproduction of the matter on the sheet. Accordingly,evenzifythe' sheets be fresh when the stencil is cut, subsequent hardening causes the production of poor copies.

One important object of the present invention is to produce a novel composition for such use which will be free from any hardening tending to stiifen the sheet to which it is applied, with the consequent tendency of the sheet to crack either 30 before or after the stencil is cut.

It is also highly desirable that such stencil sheets should be very transparent so that they may be properly positioned on thebacking or gage sheet during the cutting of the stencil.

A second important object of the invention is to provide an improved and novel composition for stencil sheets which, when applied to such sheets, willrender the sheets so transparent that when laid on printed matter or the like such matter 40 is clearly legible through the sheet.

It is frequently desirable that such stencil sheets be of a selected color and a third important object of the invention is to provide a novel and improved composition for stencil sheets which may be mixed with a suitable coloring material to color or dye the sheets without markedly interfering with the desirable transparency.

In the compositions now commonly used for this purpose oxidiz'able ingredients prevail and the compositions are not such as to prevent such oxidization.

A fourth important object of the invention is to provide a novel composition for this purpose wherein the combination of ingredients is such as j to eliminate undesirable oxidization.

With the above and other objects in view, as willbe hereinafter apparent, the invention consists in general of a novel composition for coating and impregnating stencil sheets, which com- 0 position when applied renders such sheets highly 5 fle'xiblaenables clear stencils to be cut by any of the manipulations used for the purpose and which does notmaterially change with age.

In making such compositions it has been found that a resin varnish forms an admirable base for 10 this purpose when mixed with certainother ingredients and for this base I employ such a resin gum dissolved in a volatile solvent. Although the invention is not restricted thereto I may use a copal gum such as Manilla gum and may dissolve this gum in sulphuric ether, methyl alcohol, ethyl alcohol or a mixture of two'or more of suchsolvents. Preferably the solution when madeis allowed to settle and the supernatant clear fluid only is used. Such a base, by itself, if applied to the paper co'mmonly used for stencil sheets, this paper being known to the trade as Yosln'no paper, and dried as usual, is not sufiiciently penetrable to enable stencils to be clearly cut. I therefore mix with the base thus formed a mixture of tri- 5 acetin and di-butyl phthalate. The effect of the triacetin is to make the coated sheet readily penetrable to the cutting effect of the blows of typewriter type, pressure of a stylus or the like. It has been found that the addition of di-butyl phthalate 3Q renders the triacetin more readily miscible with the base and at the same time inhibits oxidization in the mixture. Di-butyl phthalate is a non-drying oily liquid and in the present composition triacetin acts as an emollient to prevent hardening of the gum. It is to be understood therefore that the invention is not restricted to the use of these specific ingredients as other suitable emollients and non-drying oils may be used.

It has been found that, for the specific ingre- 40 clients above mentioned the mixture may be made in the following proportions:-

Solution of copal gum 3 drams Triacetin l% drams Di-butyl phthalate /2 dram when added after the other ingredients have been mixed.

The ingredients having been mixed, the sheets of paper are treated in the usual manner and the solvent of the gum allowed to evaporate. Stencil sheets thus prepared are highly flexible, aiford clearly cut' stencils and have no appreciable deterioration with age.

It is to be noted that the use of di-butyl phthalate alone with a gum results in a non-drying composition which cannot be used for this purpose. Also, the use of triacetin alone with a gum is undesirable because the coated sheetquickly hardens through oxidation of the triacetin. It is important and essential therefore that triacetin or its equivalent and di-butyl phthalate or its equivalent should be combined with the gum so that their actions balance each other. Moreover, this composition produces a clearly transparent sheet when applied to the usual fibre sheet or paper.

It is highly essential that the ingredients of the mixture as above noted be combined in the following manner by adding during agitation /2 dram di-butyl phthalate into 1 ,5; drams triacetin andslowly adding this latter solution-during agitation to the 3 drams of copal gum solution until the entire quantity is in complete solution and ready for use for making a homogeneous coating for stencil sheets.

To obtain the desired results, theseingredients must be combined in the order above set forth, namely, one half dram of di-butyl phthalate-mixed into one and one-quarter drams of triacetin during agitation. This produces a clear transparent mixture but a reversal of this order of the mixing steps would result in a mixture that'is'milky or curdled and undesirable for this purpose. The slow addition of this mixture to the three drams of copal gum solution during agitation completes the stencil coating composition ready for use.

It is obvious that changes may be made in the specific ingredients used and the proportions given without departing from the spirit of the invention. It is not, therefore, desired to confine the invention to such specific ingredients and proportions but it is desired to include all such as come within the scope of the appended claims. a 1 I I What is claimed is:

' 1. A composition for stencil sheets including a base of copal gum, triacetin, and di-butyl "phthalate, in substantially the following proportions: copal gum in solution, 3 drams, triacetin, 1%, drams, di-butyl phthalate, dram.

2.' A method of forming a homogeneous coating for stencil sheets consisting in mixing into a solution of 1 /4 drams triacetin, A; dram di-butyl phthalate by agitation of the triacetin while slow- 1y adding the di-butyl phthalate thereto, and then slowly adding said solution into 3 drams of copal gum solution during agitation until the mass is in completev solution.

3. The process of preparing a coating for stencils'consisting in first mixing dibutyl phthalate intoa relatively larger amount of triacetin during agitation and then mixing slowly into copal gum solution by further agitation.

4. The process of preparing a coating for stencils consisting in first mixing one-half part of dibutyl phthalate into one and one-quarter parts of triacetin during agitation and then mixing slowly into copal gum solution by further agitation.

5. The process of preparing a stencil coating consisting in mixing into a solution a half part of di-butyi phthalate and about one and one-quarter parts of triacetin. by agitation of the triacetin while slowly adding'the bi-butyl phthalate thereto, and then slowly adding said solution into about three parts of copal gum solution during agitation.

ROBERT O. WILLIAMS. 

